Proppants or propping agents are widely used to maintain permeability in oil and gas wells. Proppants are materials that can be dispersed in a carrier liquid and pumped into oil or gas wells under pressure during a fracturing process. Proppants can “prop” open fractures in the rock formation surrounding the wellbore and thus preclude such fractures from closing. As a result, the amount of formation surface area exposed to the wellbore can be increased, enhancing recovery rates. Proppants can also add mechanical strength to the formation and thus help maintain flow rates over time.
Proppants can provide additional functionality to cover such uses as tracking or tracing the characteristics of the proppant pack. For example, Nguyen et al. (U.S. Patent Application Publication No. US 2005/0274510 A1) describes the use of a particular conductive polymer and/or conductive filler phase in a polymer coated proppant to determine formation parameters via an electric field-based remote sensing procedure. In another example, Ayoub et al. (U.S. Pat. No. 7,082,993 B2) describes the use of active or passive devices to characterize fracture parameters. These two methods do not take into account the extreme and often hostile environment down hole in a typical hydrocarbon well system, which would necessarily lead to degradation and/or failure of the tracking device deployed in such situations. For example, extreme temperatures and pressures can lead to the degradation of polymeric based systems and active electronic devices as proposed in Ayoub et al.
McCarthy et al. (U.S. Patent Application Publication No. US 2006/0102345 A1) describes a proppant tracking and fracture zone characterization material. This material is essentially an additional particle or filler that is added to a proppant pack to enable sensing of the proppant pack. As the particles are generally smaller than the proppant particles themselves, there exists the possibility of “plugging” interstitial sites in the proppant-filled formation, thus leading to degradation of overall permeability of the proppant pack.
The above approaches collectively exhibit a combination of the following characteristics: poor proppant transport inhibiting both well performance (flow rates) and fracture imaging; poor conductivity under load, particularly at typical reservoir depths (i.e. greater than 1,000 feet); poor longevity due to attack by temperature, corrosion, stress cycling, or absolute closure stress; and poor signal to noise ratios precluding surface assessment requiring costly investment in offset wells or down hole measurement devices. In some cases, this precludes effective imaging of propped fracture length, width, and height. In the worst case, only two of these three dimensions can be imaged. In addition, in the above approaches, the specific gravities of the proppant and that of the sensing element or particle are not able to be matched, thus it becomes impossible to obtain a homogeneous mix of proppant and sensing particles within the proppant pack when placed in the formation.
A need exists for proppants having additional functional properties beyond serving to prop open subterranean fractures. A need also exists for methods to accurately map a fracture in three dimensions using above ground detection systems.